U.S. Pat. No. 6,322,612 (Air Products) describes a pressure or vacuum swing adsorption process and apparatus used for the separation and recovery of certain gaseous components, such as carbon dioxide from hot gas mixtures containing water vapour. The process comprises reacting the feed gas mixture at a temperature of between 150 and 450° C. in an adsorber column containing an adsorbent. The adsorbent can be sodium-promoted alumina or potassium-promoted hydrotalcite and adsorbs the carbon dioxide. The adsorbent is regenerated by depressurising and then purging the absorber column with steam to withdraw an effluent comprising a mixture of carbon dioxide and possible further adsorbable components, and H2O. Next, the adsorber column is pressurized by introducing a gas that is depleted of carbon dioxide. The steps are repeated in a cyclic manner.
WO 2010/059052 describes a sorption-enhanced water gas shift (SEWGS) process to produce hydrogen and carbon dioxide as well as hydrogen sulphide, wherein the carbon dioxide and hydrogen sulphide are adsorbed onto an alkali promoted hydrotalcite adsorbent. The carbon dioxide and hydrogen sulphide are subsequently simultaneously removed from the adsorbent.
In these and other prior art processes using acidic adsorbents, acidic gaseous components such as carbon dioxide, hydrogen sulphide and the like end up in the same product (or effluent) stream, which make reuse or purification of these streams difficult. The problem to be solved by the invention is a stepwise and selective removal of gaseous acidic species for adsorbents used for producing desirable-especially hydrogen-containing-gas mixtures.